A very large number of transition metal complexes are known which catalyse the hydrogenation of unsaturated compounds and which are soluble in suitable organic solvents or in the reactants and in the hydrogenation products. Those catalysts are dealt with in an article in "Principles and Applications of Organotransition Metal Chemistry", by J. P. Collman, University Science Books, Mill Valley, U.S.A.
United States patent U.S. Pat. No. 3,565,823 describes a composition consisting of a dispersion constituted by a compound, in particular of a transition metal in a salt of tin or germanium and a quaternary ammonium or phosphonium. U.S. Pat. No. 3,657,368 describes an olefin hydrogenation process and U.S. Pat. No. 3,919,271 describes a nitrile hydrogenation process, both using the above composition. U.S. Pat. No. 3,832,391 claims an olefin carbonylation process using the same composition.
The compositions described above have the disadvantage of having a relatively high melting point, the hydrogenation reaction thus taking place at 50.degree. C., for example.